i.11.6 Triple integrals

Calculate the mass of a body \( V \) with density \( \rho \) bounded by these planes: \[ \begin{array}{l} V: x=0, \quad y=0, \quad x+y+z=1 ; \\ \rho(x, y, z)=\frac{1}{(1+x+y+z)^{3}} . \end{array}\]